Polymer film for wrapping a stent structure

ABSTRACT

The drug loaded stent includes an expandable stent structural member, and a planar sheet of polymeric material attached to the outside of the expandable stent structural member. The polymeric material is preferably bioabsorbable, and loaded or coated with a therapeutic agent or drug to reduce or prevent restenosis in the vessel being treated. The polymer material can be attached to the metal stent at one or more points, and wrapped in a coil around the stent in an unexpanded state, to uncoil and expand in diameter to substantially match the expanded diameter of the metal stent; or can be wrapped tightly around the stent structural member and attached to itself, to stretch radially when the stent structural member is expanded. In another currently preferred embodiment, a combination of a stent structural member and a polymeric film wrapping can be provided with a coating of lubricious material. The lubricious material can be polyethylene oxide, polyethylene glycol, polyethylene acetate, polyvinyl pyrrolidone, polyvinyl alcohol, polyacrylamide, hydrophilic soft segment urethanes, some natural gums, polyanhydrides or other similar hydrophilic polymers, and combinations thereof. The layer of lubricious material protects the stent from the guide or the body lumen in which the stent is inserted by providing a low friction surface over the stents.

This is a continuation of application Ser. No. 08/355,402, filed Dec.13, 1994 and now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to expandable intraluminal vasculargrafts, generally referred to as stents, and more particularly concernsmetal stents wrapped with a polymer film capable of carrying andreleasing therapeutic drugs.

2. Description of Related Art

Stents are typically implanted within a vessel in a contracted state andexpanded when in place in the vessel in order to maintain patency of thevessel to allow fluid flow through the vessel. Ideally, implantation ofsuch stents is accomplished by mounting the stent on the balloon portionof a catheter, positioning the stent in a body lumen, and expanding thestent to an expanded state by inflation of a balloon within the stent.The stent can then be left in place by deflating the balloon andremoving the catheter.

Stents commonly have a metallic structure to provide the strengthrequired to function as a stent, but typically do not provide for thedelivery of localized therapeutic pharmacological treatment of a vesselat the location being treated with the stent. Polymeric materialscapable of absorbing and releasing therapeutic agents may not fulfillthe structural and mechanical requirements of a stent, especially whenthe polymeric materials are loaded with a drug, since drug loading of apolymeric material can significantly affect the structural andmechanical properties of the polymeric material. Since it is oftenuseful to provide localized therapeutic pharmacological treatment of avessel at the location being treated with the stent, it would bedesirable to combine such polymeric materials with existing stentstructures to provide a stent with the capability of absorbingtherapeutic drugs or other agents, for placement and release of thetherapeutic agents at a specific intravascular site. The presentinvention meets this need.

SUMMARY OF THE INVENTION

Briefly, and in general terms, the present invention provides for astent wrapped with a polymer film capable of carrying and releasingtherapeutic agents. Since the polymer film is wrapped on the outside ofthe stent, and is not needed to provide structural strength to assist inopening the flow path of the vasculature or other body lumen where thestent is to be placed, the drug-containing section can be speciallyformulated for its specific function of delivering drugs locally. Thestent can be used in coronary arteries or any other part of thevasculature or other body lumen where mechanical opening force isnecessary or desirable to keep the vessel open or to maintain the stentflush against the lumen wall, and where an anti-restenosis,anti-proliferative or other types of therapeutic drug or agent is to besimultaneously positioned and diffused.

The invention accordingly provides for a drug loaded stent, comprisingan expandable stent structural member, and a planar sheet of polymericmaterial disposed on the outside of the expandable stent structuralmember. The polymeric material is preferably bioabsorbable, and ispreferably loaded or coated or laminated with a therapeutic agent ordrug to reduce or prevent restenosis and thrombosis in the vessel beingtreated. The polymer material can be a thermoplastic or an elastomer,for example, so that the film can stretch or deform radially when thestent structural member is expanded. The film of polymer material can beformed as a solid sheet, or can incorporate holes of various sizes andshapes to promote rapid endothelialization.

The polymer film is preferably mounted to the stent structural member,and in a presently preferred embodiment, the polymer film can beattached to the existing stent structural member in an unexpanded stateby adhesive or by heat sealing, with the stent structural membersandwiched between internal and external layers of film heat sealedaround the stent structural member, or mechanically, such as bymechanical connection such as by hooking one or more slots on an edgeportion of the polymeric material through a corresponding slottedportion of the stent structural member, or with a metal clip. Thepolymer material can be attached to the stent structural member at oneor more points, and wrapped in a coil around the stent in an unexpandedstate, so that the diameter of the outer coiled film would uncoil andexpand in diameter to match the diameter of the metal stent. When coiledaround the stent structural member, the coiled polymer film can have atleast one slit transverse to the longitudinal axis about which the stentis coiled to accommodate possible uneven expansion of the underlyingstent structural member.

In another presently preferred embodiment, the polymer material can beattached to an existing stent structural member by an interference fitby tightly wrapping the polymer film at least once circumferentiallyaround the stent structural member in an unexpanded state and attachingthe polymer film to itself to form a sleeve around the stent structuralmember, such as by heating and melting the film to itself, adhesivebonding, solvent bonding, bonding one or more strips of elasticpolymeric material on the outside edge of the polymeric film wrap tosecure it, or by mechanical fastening, such as by a clip.

In one currently preferred embodiment, the polymer material can beattached to an existing stent structural member by hooking one or moreslots on an edge portion of the polymeric material through acorresponding slotted portion of the stent structural member, tightlywrapping the polymer film at least once circumferentially around thestent structural member in an unexpanded state to form a coil of layersof the polymeric material, and securing the layers in a tightly wrappedcoil. The coil is currently preferably secured to the stent structuralmember by adhesive bonding, typically by an adhesive such as a copolymerof poly-L-lactic acid (L-PLA) and polycaprolactone (PCL), although otheradhesives, heat bonding, solvent bonding, or one or more mechanicalfasteners, such as with a metal clip, for example, may also be suitable.Alternatively, the coil can be secured in a tightly wrapped coil byattaching one end of at least one piece of elastic material to anexterior end portion of the coil of polymeric material, and attachingthe other end of the elastic material to a portion of the exterior ofthe wrapped coil of polymeric material. The elastic material stretchesto allow the coil of polymeric material to uncoil as the stent isexpanded.

In another currently preferred embodiment, a combination of a stentstructural member and a polymeric film wrapping can be provided with acoating of lubricious material. The lubricious material currentlypreferably comprises a mixture of polyethylene oxide and polyethyleneglycol, although other types of hydrophilic polymeric materials such aspolyethylene acetate, polyvinyl pyrrolidone (PVP), polyvinyl alcohol,polyacrylamide, hydrophilic soft segment urethanes, some natural gumssuch as gum arabic, gum tragacanth and the like, polyanhydrides or othersimilar hydrophilic polymers, and combinations thereof, can also beused. The lubricious coating is currently preferably applied over astent and polymer film wrap combination by dipping the wrapped stent inthe hydrated, liquid lubricious material. The layer of lubriciousmaterial protects the stent from the guide or the body lumen in whichthe stent is inserted by providing a low friction surface over thestent.

These and other aspects and advantages of the invention will becomeapparent from the following detailed description, and the accompanyingdrawings, which illustrate by way of example the features of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a first embodiment of the stentstructural member and film of polymer material of the drug loaded stentof the invention shown in an unexpanded state;

FIG. 2 is a cross-sectional view of the drug loaded stent of FIG. 1shown in an expanded state;

FIG. 3 is a perspective view of the drug loaded stent of FIG. 1;

FIG. 4 is a perspective view of an alternate embodiment of the drugloaded stent of FIG. 1 having apertures in the exterior sheet ofpolymeric material;

FIG. 5 is a cross-sectional view of a second embodiment of the drugloaded stent of the invention, shown in an unexpanded state;

FIG. 6 is a perspective view of an alternate embodiment of the drugloaded stent of FIG. 5 having apertures in the polymeric material;

FIG. 7 is a cross-sectional view of an alternate embodiment of the drugloaded stent of FIG. 5 having multiple wrappings of the polymericmaterial;

FIG. 8 is an elevational view of a representative stent structuralmember, shown in a vessel;

FIG. 9 is a plan view of a sheet of polymeric material in anotheralternative embodiment including elastic strips for securing thepolymeric material wrapped around a stent structural member;

FIG. 10 is a cross-sectional view of a drug loaded stent wrapped withthe polymeric material of FIG. 9;

FIG. 11 is a perspective view of the drug loaded stent of FIG. 10;

FIG. 12 is a plan view of a sheet of polymeric material in a furtheralternative embodiment including an elastic strip extending the width ofthe polymeric material for securing the polymeric material when wrappedaround a stent structural member;

FIG. 13 is a perspective view of a drug loaded stent wrapped with thepolymeric material of FIG. 12;

FIG. 14 is a plan view of a sheet of polymeric material in a furtheralternative embodiment including attachment tabs for securing thepolymeric material to a stent structural member;

FIG. 15 is an elevational view of a drug loaded stent wrapped with thesheet of polymeric material of FIG. 14 and mounted on a balloondilatation catheter for delivery;

FIG. 16 is an enlarged partial sectional view of the drug loaded stentof FIG. 15 showing the sheet of polymeric material wrapped around aslotted tube stent structural member;

FIG. 17 is an elevational view of the drug loaded stent of FIG. 15covered with a layer of a lubricious, hydrophilic polymeric coating; and

FIG. 18 is a partial sectional view of the drug-loaded stent of FIG. 17.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Stents that have a metallic structure typically do not provide for thedelivery of localized therapeutic drugs in a blood vessel, whilepolymeric materials that can be used for drug delivery may not fulfillthe structural and mechanical requirements of a stent to hold open abody lumen. Polymeric materials used for the dual function of structuralsupport and for absorbing and releasing therapeutic agents may notfulfill either function satisfactorily, since drug loading of apolymeric material can significantly affect the structural andmechanical properties of the polymeric, material, and the ability toabsorb and release therapeutic agents or drugs can affect structuralcharacteristics.

Accordingly, as shown in FIGS. 1-4, the present invention provides for astent 20 that can be drug loaded, comprising an expandable stentstructural member 22, and a planar sheet or film 24 of polymericmaterial, further described below, that in a first embodiment isattached to the metal stent at one or more points of attachment 26, andis wrapped in a coil around the stent in an unexpanded state. Thepolymer material can be extruded as a thin film, and any processing canbe done while the material is a flat sheet.

The attachment of the film of polymeric material to the stent structuralmember in an unexpanded state can be by adhesive, heat sealing, such aswith the stent structural member sandwiched between internal andexternal layers of film heat sealed or otherwise laminated around thestent structural member, by mechanical connection such as by hooking oneor more slots on an edge portion of the polymeric material through acorresponding slotted portion of the stent structural member, as will bedescribed further below, or with a metal clip, for example. The film ofpolymeric material also has a free end 28, and can have one or moreslits 30 in the polymeric film transverse to the axis 32 of the stent toaccommodate possible uneven expansion of the underlying stent structuralmember. The planar sheet of polymeric material is preferably adapted touncoil and expand to match the expansion of the stent structural member.The planar sheet of polymeric material can be a solid sheet, or also canhave a surface defining a plurality of apertures 34 of various sizes andshapes to promote rapid endothelialization, as is illustrated in FIG. 4.The stent can be mounted on a balloon dilatation catheter, fordeployment of the stent in the vasculature of a patient.

As is illustrated in FIG. 5, in a second embodiment of the stent 40 thatcan be drug loaded, the stent comprises a stent metal structural member42, and a planar sheet or film of polymeric material 44, furtherdescribed below. The film of polymeric material in this embodiment has afirst end 46 forming a first layer 47 of the polymeric material, and asecond end 48 overlapping the first end forming a second layer 49 andattached to the first layer of the polymeric film, preferably by heatingand melting the film to itself to form a longitudinal heat seal bond 50between the first and second layers. Attachment of the two outer layersof the polymeric film can also be accomplished by adhesive bonding,solvent bonding, or one or more mechanical fasteners, such as with ametal clip, for example. In this embodiment, the planar sheet ofpolymeric material is preferably wrapped circumferentially and cinchedtightly as a sleeve around the stent structural member, and is thusattached to the stent structural member by interference fit. In analternative embodiment illustrated in FIG. 7, the polymeric material canbe wrapped multiple times around the stent to form multiple layers thatcan be joined together as described with reference to FIG. 5 to form atube around the stent. Alternatively, the polymeric material can beformed as a seamless tube or sleeve to fit tightly around the unexpandedstent structural member.

The primary function of the sheet of polymeric material is to delivertherapeutic agents or drugs to help prevent thrombosis and/orrestenosis. The planar sheet of polymeric material is preferablyselected from the group of polymers consisting of thermoplastic andelastomeric polymers, so that the polymeric film can stretch or deformradially when the stent structural member is expanded.

As is shown in FIG. 6, the planar sheet of polymeric material also canhave a surface defining a plurality of apertures 52 of various sizes andshapes to promote rapid endothelialization, similar to the embodimentillustrated in FIG. 4. The stent can be mounted on a balloon dilatationcatheter, for deployment of the stent in the vasculature of a patient.

In each of these embodiments, the stent structural member is of the typethat can be implanted within a vessel in a contracted state and expandedto maintain patency of the vessel and to allow fluid flow through thevessel, such as expanding stents available from Advanced CardiovascularSystems, Inc., Santa Clara, Calif., (ACS), Palmaz-Shatz (Johnson andJohnson), Gianturco (Cook Incorporated), and the like. The metalstructural member can, for example, be formed from a metal selected fromthe group of metals consisting of stainless steel, MP35N, MP20N,elastinite (nitinol), tantalum, nickel-titanium alloy, platinum-iridiumalloy, gold, and magnesium, although the stent structural member canalso be formed of suitable non-metallic materials. "MP35N" and "MP20N"are trade names for alloys of cobalt, nickel, chromium and molybdenumavailable from Standard Pressed Steel Co. of Jenkintown, Pa. MP35Nconsists of 35% cobalt, 35% nickel, 20% chromium, and 10% molybdenum.MP20N consists of 50% cobalt, 20% nickel, 20% chromium, and 10%molybdenum. A representative stent structural member 60 with which asheet of polymeric material can be combined according to the principlesof the invention is illustrated in FIG. 8. In one preferred embodiment,the stent structural member 60 can be formed of metal, and comprises aplurality of radially expandable cylindrical elements 62 disposedcoaxially and interconnected by members 63 disposed between adjacentcylindrical elements. The stent structural member is shown without acovering sheet of polymeric material, in a typical setting within avessel 65, for repairing a detached vessel lining 66, for example, andmaintaining the patency of the vessel.

The polymeric material is preferably selected from thermoplastic andelastomeric polymers. In one currently preferred embodiment thepolymeric material can be a material available under the trade name"C-Flex" from Concept Polymer Technologies of Largo, Fla. In anothercurrently preferred embodiment, the polymeric material can be ethylenevinyl acetate (EVA); and in yet another currently preferred embodiment,the polymeric material can be a material available under the trade name"BIOSPAN." Other suitable polymeric materials include latexes,urethanes, polysiloxanes, and modified styrene-ethylene/butylene-styreneblock copolymers (SEBS) and their associated families, as well aselastomeric, bioabsorbable, linear aliphatic polyesters. The polymericmaterial can typically have a thickness in the range of about 0.002 toabout 0.020 inches, for example. The polymeric material is preferablybioabsorbable, and is preferably loaded or coated with a therapeuticagent or drug, including, but not limited to, antiplatelets,antithrombins, cytostatic and antiproliferative agents, for example, toreduce or prevent restenosis in the vessel being treated. Thetherapeutic agent or drug is preferably selected from the group oftherapeutic agents or drugs consisting of sodium heparin, low molecularweight heparin, hirudin, argatroban, forskolin, vapiprost, prostacyclinand prostacyclin analogues, dextran, D-phe-pro-arg-chloromethylketone,dipyridamole, glycoprotein IIb/IIIa platelet membrane receptor antibody,recombinant hirudin, thrombin inhibitor, angiopeptin, angiotensinconverting enzyme inhibitors, (such as Captopril, available from Squibb;Cilazapril, available for Hoffman-La Roche; or Lisinopril, availablefrom Merck) calcium channel blockers, colchicine, fibroblast growthfactor antagonists, fish oil, omega 3-fatty acid, histamine antagonists,HMG-CoA reductase inhibitor, methotrexate, monoclonal antibodies,nitroprusside, phosphodiesterase inhibitors, prostaglandin inhibitor,seramin, serotonin blockers, steroids, thioprotease inhibitors,triazolopyrimidine and other PDGF antagonists, alpha-interferon andgenetically engineered epithelial cells, and combinations thereof. Whilethe foregoing therapeutic agents have been used to prevent or treatrestenosis and thrombosis, they are provided by way of example and arenot meant to be limiting, as other therapeutic drugs may be developedwhich are equally applicable for use with the present invention.

In another currently preferred embodiment illustrated in FIGS. 9-13, thestent 70 that can be drug loaded comprises a stent metal structuralmember 72, such as the stent structural member 70 illustrated forexample in FIG. 8, and a planar sheet or film of polymeric material 74,preferably including a plurality of apertures 88, as will be furtherexplained below. The polymeric material can be attached to an existingstent structural member by tightly wrapping the polymer film at leastonce, and preferably multiple times, circumferentially around the stentstructural member 72 in an unexpanded state to form a coil of layers ofthe polymeric material. The film of polymeric material in thisembodiment has an interior end 76, multiple wrappings forming aplurality of layers 77 of the polymeric material, and an exterior end 78overlapping the multiple layers. The coil of polymeric material ispreferably secured snugly over the stent structure by at least one pieceor strip of elastic material 80. One end 82 of at least one such pieceor strip of elastic material is attached to the exterior end portion 78of the coil of polymeric material, and an opposing end 83 of the pieceof elastic material is attached to another portion 84 of the exterior ofthe wrapped coil of polymeric material, across edge of the exterior endportion 78 of the coil of polymeric material, to secure the coil on thestent. In one currently preferred embodiment illustrated in FIGS. 9-11,the coil of polymeric material can be advantageously secured on thestent structural member by two strips of such elastic material.Additional strips of elastic material can also be used to secure thecoil of polymeric material, as needed. The elastic material stretches toallow the coil of polymeric material to uncoil as the stent is expanded.In a currently preferred embodiment, the strips of elastic material areheat bonded to the coil of polymeric material. Attachment of the elasticmaterial can also be accomplished by adhesive bonding, solvent bonding,or one or more mechanical fasteners, such as with a metal clip, forexample. In this embodiment, the planar sheet of polymeric material ispreferably wrapped circumferentially and cinched tightly as a sleevearound the stent structural member, and is thus attached to the stentstructural member by interference fit.

In a currently preferred alternative embodiment shown in FIGS. 12 and13, similar to that illustrated in FIGS. 9-11, the elastic strip ofmaterial 80 can extend and be bonded along the entire width of theexterior end 78 of the coil of polymeric material as is shown in FIG.12, and can be bonded to the other portion 84 of the exterior of thewrapped coil of polymeric material, across the edge of the exterior endportion 78 of the coil of polymeric material, to secure the coil on thestent, as is illustrated in FIG. 13. The strip of elastic material canalso be perforated, such as with apertures 86 formed in the strip ofelastic material for example, to decrease the cross-sectional area ofthe elastic material, to permit the elastic material to stretch moreeasily. The polymeric film material also currently preferably includes aplurality of apertures 88 so that the polymeric material is porous, toallow blood flow through the stent structural member to the vessel wall,such as for oxygenation and nutrient exchange to the vessel wall, and inorder to present a decreased surface area for purposes of reducingthrombogenicity. The apertures also improve the flexibility of thepolymeric material, allowing the stent segment to be more easily rolledand uncoiled during expansion of the stent structural member, and alsofacilitate the process of cell growth over the surface of the stent.

The primary function of the sheet of polymeric material is to delivertherapeutic agents or drugs to help prevent thrombosis and/orrestenosis. The planar sheet of polymeric material is preferablyselected from the group of polymers consisting of thermoplastic andelastomeric polymers, that however can be substantially inelastic, so asnot to lose a significant part of their thickness during expansion ofthe stent structural member, such as polycaprolactone, for example,allowing a high upper threshold for the amount of one or more drugs thatcan be loaded in the polymeric material and delivered. The inelasticpolymeric material currently preferably is of a thickness that willguarantee drug delivery over at least approximately a seven day period,which is not currently possible with radially expanding elastic films.In the embodiment illustrated in FIGS. 9-13, an inelastic drug loadedpolymeric material is currently preferably no greater than about 0.002inch thick, and typically approximately 0.0015 inch to 0.002 inch thick,to prevent the profile of the stent and wrap of polymeric material frombecoming too large. The elastic portion of the sleeve of polymericmaterial keeps the coiled polymeric film secured snugly over theexpandable stent structural member, so that the polymeric material canbe applied over the stent structural member without the need foradditional internal points of attachment to the stent structural member.The elastic portion of the sleeve of polymeric material also keepstension on the coiled, inelastic drug-containing material while thestent structural member is expanding, without providing so muchresistance so as to impede expansion of the stent structural member, orthe unrolling of the inelastic polymeric material.

The elastic strip of material can be joined on the interior or exteriorof the end portion of the coiled polymeric material. The elasticmaterial attached over the coil of polymeric material helps keep thecoil of drug loaded material snug on the stent structural member beforeit is expanded, and guides its linear expansion during inflation of aballoon dilatation catheter used for deployment of the stent andpolymeric drug loaded material in the vasculature or other body lumen ofa patient.

The elastic material is currently typically formed of ethylene vinylacetate, but can also be formed of silicone polymers. The drug loadedlayer of polymeric material, and the stent structural member can beformed of the materials as described above in the previous embodiments.

In another alternative embodiment illustrated in FIGS. 14-16, anotherpreferred type of stent 90 that can be drug loaded comprises a stentmetal structural member 92, that can for example be a slotted tube typeof stent having a plurality of slotted openings 91 and structural ribs93 as is illustrated in FIG. 16, such as is available from ACS forexample, in combination with a planar sheet or film of polymericmaterial 94. The stent structural member can also be other types ofstents that preferably have a relatively significant proportion of spaceprovided by openings, slots, or the like in the otherwise solid materialof the stent structure. The polymeric material can be attached to such astent structural member by tightly wrapping the polymer film at leastonce, and preferably multiple times, circumferentially around the stentstructural member 92 in an unexpanded state to form a coil of layers ofthe polymeric material. The film of polymeric material in thisembodiment has an interior end 96 with at least one attachment member ortab 100 adapted to be received in openings 91 of the stent structuralmember and thereby attached to the stent structural member, and providesmultiple wrappings forming a plurality of layers 97 of the polymericmaterial, with an exterior end 98 overlapping the interior multiplelayers. As is shown in FIG. 14, the polymeric film of material currentlypreferably has a plurality of attachment tabs 100, and typically has twoof the attachment tabs. Each attachment tab currently preferablyincludes an aperture 101 therethrough adapted to receive and hook onto astructural rib portion 93 of the stent structural member. The attachmenttab also includes a slit 102 extending from the aperture 101 to theouter edge 103 of the attachment tab to allow the attachment tab to behooked onto the stent structural member. After the attachment tab ishooked onto a portion of the stent structural member, the slit 102 ispreferably sealed closed, such as by application of an adhesivematerial, typically a copolymer of poly-L-lactic acid (L-PLA) andpolycaprolactone (PCL), other suitable adhesives, or by heat bonding.The coil of polymeric material is preferably formed of a thermoplasticmaterial such as polycaprolactone that can be drug loaded, and can bewrapped and secured snugly over the stent structure by heat bonding theexterior end 98 to another portion of the exterior of the wrapped coilof polymeric material as described above. The polymeric film of materialtensions the attachment tabs as the stent structural member is expandedand as the wrapping of polymeric material uncoils, to bias theattachment tab extending into the lumen of the stent structural memberagainst the inner surface of the lumen of the stent structural member toensure that the attachment tabs do not obstruct the lumen within thestent structural member. Attachment of the exterior edge of thepolymeric material to the wrapping of polymeric material is currentlypreferably accomplished by adhesive bonding, typically by an adhesivesuch as a copolymer of poly-L-lactic acid (L-PLA) and polycaprolactone(PCL), although other adhesives, heat bonding, solvent bonding, or oneor more mechanical fasteners, such as with a metal clip, for example,may also be suitable.

In a currently preferred embodiment, the polymeric film material istypically about 0.002 inch thick, and also currently preferably includesa plurality of apertures 108 so that the polymeric material is porous,to allow blood flow through the stent structural member to the vesselwall, such as for oxygenation and nutrient exchange to the vessel wall,and in order to present a decreased surface area for purposes ofreducing thrombogenicity. The apertures also improve the flexibility ofthe polymeric material, allowing the stent segment to be more easilyrolled and uncoiled during expansion of the stent structural member, andalso facilitate the process of cell growth over the surface of thestent.

The primary function of the sheet of polymeric material is to delivertherapeutic agents or drugs to help prevent thrombosis and/orrestenosis. The planar sheet of polymeric material is preferablyselected from the group of polymers consisting of thermoplastic andelastomeric polymers that may be inelastic, and that do not lose asignificant part of their thickness during expansion of the stentstructural member, allowing a high upper threshold for the amount of oneor more drugs that can be loaded in the polymeric material anddelivered. As is illustrated in FIGS. 15 and 16, the drug loaded stentcan be mounted on an expandable balloon member 110 of a dilatationcatheter 112, near radiopaque markers 114 of the catheter, for deliveryof the stent in an artery, blood vessel, or other body lumen, such asthrough a protective sheath 116, shown cutaway for convenience ofillustration.

In another currently preferred embodiment illustrated in FIGS. 17-18, acombination of a stent structural member and a polymeric film wrappingcan be provided with a coating of lubricious material 120. Thelubricious material currently preferably comprises a mixture ofpolyethylene oxide and polyethylene glycol, providing both high and lowmolecular weight components in the lubricious material, although othertypes of hydrophilic polymeric materials such as polyethylene acetate,polyvinyl pyrrolidone (PVP), polyvinyl alcohol, polyacrylamide,hydrophilic soft segment urethanes, some natural gums such as gum arabicor gum tragacanth and the like, polyanhydrides or other similarhydrophilic polymers, and combinations thereof, can also be used. Thelubricious material can also carry an anti-thrombogenic drug that can bethe same as, or complementary to, the anti-thrombogenic oranti-proliferative drug or drugs carried in the polymeric material ofthe stent.

The lubricious coating is currently preferably applied over a stent andpolymer film wrap combination by dipping the wrapped stent in thehydrated, liquid lubricious material. The lubricious material istypically prepared to be sufficiently viscous to allow the stent to besufficiently coated by a single dipping. The lubricious coating isinitially quite sticky when applied, but is dried to provide anon-sticky tight cocoon around the wrapped stent, and helps to keep thepolymer wrapping tight. While the lubricious coating is shown applied toa wrapped stent such as that of FIGS. 14-16, the lubricious coating canadvantageously be applied to any of the foregoing Wrapped stentcombinations, and other suitable stents as well. The lubricious coatingbecomes hydrated again upon exposure to the blood during delivery of thestent. When a sheath is used in the delivery system to protect the stentduring delivery, the lubricious coating can be initially hydrated beforecontacting the blood by flushing the sheath with saline solution. Due tothe gel-like nature of the lubricious coating, the lubricious coatingeventually dissolves in a short period of time, and will typically becompletely degraded and dissolved by the time that the stent is deployedand expanded.

The layer of lubricious material protects the stent from the guide orthe anatomy by providing a low friction surface over the stent. If asheath or sleeve is used for delivering the stent, the lubriciouscoating aids in retraction of the sheath by decreasing friction betweeninternal and external layers of the delivery system. The deployment ofthe stent can also be improved by decreasing friction between the stentand the balloon used to deliver the stent, decreasing friction betweenthe layers of the stent itself, or decreasing friction between thevessel or lumen wall and the stent. The need for a sheath for protectingthe stent during delivery can also be mitigated if the coating is of athickness suited to providing a smooth transition through the deliverysystem, and still provides a low profile of the uninflated, undeployedstent. Alternatively, the lubricious coating can also be formed as adried sheet of lubricious material, cut into a strip, wrapped in spiralfashion over the length of the polymeric drug carrying wrapping, andbonded in place by an adhesive such as a copolymer of poly-L-lactic acid(L-PLA) and polycaprolactone (PCL), although other adhesives, or heatbonding may also be suitable.

It has thus been demonstrated that the invention provides for a stentcombining polymeric materials with stent structures with the capabilityof absorbing therapeutic drugs or other agents, for placement andrelease of the therapeutic agents at a specific intravascular site. Acomplex locking design is not needed, and the stent can be re-dilated ifnecessary. The polymeric, drug-containing section can be bioabsorbable,and can be specially formulated for its specific function of deliveringdrugs locally, since it is not necessary for the polymeric component toprovide assistance in keeping the blood vessel open. The polymericmaterial can be extruded as a film, using simple technology, and can beprocessed while the material is a flat sheet. The stent can be used incoronary arteries or any other part of the vasculature where mechanicalopening force is necessary or desirable to keep the vessel open, andwhere anti-restenosis, anti-proliferative or other types of therapeuticdrugs or agents can be useful in combatting thrombosis and restenosis.

It will therefore be apparent from the foregoing that while particularforms of the invention have been illustrated and described, variousmodifications can be made without departing from the spirit and scope ofthe invention. Accordingly, it is not intended that the invention belimited, except as by the appended claims.

What is claimed is:
 1. A drug loaded stent, comprising:an expandablestent structural member; a sheet of polymeric material disposed on thestent structural member, said sheet of polymeric material being wrappedabout the stent structural member at least one time to form a coilhaving an interior portion, an exterior portion, and an exterior endportion, said sheet of polymeric material being loaded with atherapeutic agent; and at least one strip of elastic material, one endof said at least one strip of elastic material being attached to theexterior portion of the coil, and an opposing end of the strip ofelastic material being attached to another portion of the exterior ofthe coil, said strip of elastic material extending across the exteriorend portion of the coil, to secure the coil on the stent, and such thatsaid sheet of polymeric material is free to uncoil when said stentstructural member is expanded, to substantially match the expansion ofsaid stent structural member.
 2. The drug loaded stent of claim 1,wherein said sheet of polymeric material is selected from the group ofpolymers consisting of thermoplastic and elastomeric polymers, wherebysaid sheet of polymeric material stretches radially when said stentstructural member is expanded.
 3. The drag loaded stent of claim 1,wherein said at least one strip of elastic material is heat bonded tothe exterior portion of the coil.
 4. The drug loaded stent of claim 1,wherein said at least one strip of elastic material has a surfacedefining a plurality of apertures therein.
 5. The drug loaded stent ofclaim 1, wherein said therapeutic agent is selected from the group ofsodium heparin, low molecular weight heparin, hirudin, argatroban,forskolin, vapiprost, prostacyclin, prostacyclin analogues, dextran,D-phe-pro-arg-chloromethylketone, dipyridamole, glycoprotein IIb/IIIaplatelet membrane receptor antibody, recombinant hirudin, thrombininhibitor, angiopeptin, angiotensin converting enzyme inhibitors,calcium channel blockers, colchicine, fibroblast growth factorantagonists, fish oil, omega 3-fatty acid, histamine antagonists,HMG-CoA reductase inhibitor, methotrexate, monoclonal antibodies,nitroprusside, phosphodiesterase inhibitors, prostaglandin inhibitor,serotonin blockers, steroids, thioprotease inhibitors,triazolopyrimidine, PDGF antagonists, alpha-interferon, geneticallyengineered epithelial cells, and combinations thereof.
 6. The drugloaded stent of claim 1, wherein said therapeutic agent is selected fromthe group consisting of antiplatelets, antithrombins, cytostatic andantiproliferative agents.
 7. The drug loaded stent of claim 1, whereinsaid stent structural member is formed from a metal selected from thegroup of stainless steel, tantalum, nickel-titanium alloy,platinum-iridium alloy, gold, magnesium, an alloy consisting essentiallyof about 35 percent cobalt, about 35 percent nickel, about 20 percentchromium, and about 10 percent molybdenum, and an alloy consistingessentially of about 50 percent cobalt, about 20 percent nickel, about20 percent chromium, and about 10 percent molybdenum.
 8. The drug loadedstent of claim 1, wherein said sheet of polymeric material has a surfacedefining a plurality of openings to promote rapid endothelialization. 9.The drag loaded stent of claim 1, wherein said sheet of polymericmaterial is coated with a layer of hydrophilic lubricious polymericmaterial.